Abstract:
The thermal stability, fire retardancy and basic mechanical properties, as a function of the mass fractions of the poly(vinyl chloride) (PVC) compound ingredients, can be modelled using 2nd order Scheffé polynomials. The empirical models for each response variable can be determined using statistical experimental design. The particular models for each response variable, which are selected for predictive ability using k-fold cross validation, can be interpreted using statistical analysis of the model terms. The statistical analysis of the model terms can reveal the synergistic or antagonistic interactions between ingredients, some of which have not been reported in literature. The interaction terms in the models also mean that the effect of a certain ingredient is dependent on the mass fractions of the other ingredients. Sensitivity analysis can be used to examine the overall effect of a change in a particular formulation on the response variables. The empirical models can be used to minimise the cost of the PVC compound by varying the formulation. The optimum formulation is a function of the costs of the various ingredients and the limits which are placed on the response variables. To analyse the system as a whole, parametric analysis can be used. The number of different parametric analyses which can be done is very large and depends on the specific questions which need to be answered. Parametric analysis can be used to gain insight into the complex behaviour of the system with changing requirements, as a decision making tool in a commercial environment or to determine the completeness of the different measuring techniques used to describe the thermal stability and fire retardancy of the PVC compound. Statistical experimental design allows for the above methods to be used which leads to significant time and labour savings over attempting to reach the same conclusions using the traditional one-factor-at-a-time experiments with changes in the phr of an ingredient. It is recommended that the data generated for this investigation is analysed in more detail using the methods outlined for this investigation. This can be facilitated by making the analysis of the data (and therefore the data itself) more accessible through a usable interface. The data set itself can also be expanded to include new ingredients requiring very few additional experiments. If a PVC compound that contains none of the ingredients that were used in this investigation is of interest a new separate data set needs to be generated. This can be done by following the same procedure used in this investigation. In fact the method that is used in this investigation can be generalised to optimise the proportions of the ingredients of any mixture.
